Characteristic traits of heterocyclic chemistries, such as polybenzoxazines and polybismaleimides, are considered to couple the thermal properties and fire retardance of phenolic matrices with the modular molecular design of epoxies. This combination renders benzoxazines an attractive matrix chemistry for high performance composite applications. Furthermore, benzoxazines possess the ability to form an alloy with other matrix chemistries affording tailorable physical properties and solventless processing, which provide the added benefit of environmentally-favorable manufacturing.
Compared to the current industrial batch reactor methods used to produce benzoxazine monomer and prepolymer, the novel reactor design of the present invention provides a cost-effective and environmentally-favorable technique that reduces reaction time, reduces the amount of isomer formation, and eliminates the need for any post-reaction purification steps. The ability to produce these heterogeneous syntheses in a continuous reactor via the invention also avoids batch-to-batch variations, which plagues batch reactor methods. Additionally, this novel continuous high shear reactor methodology is a viable technique for up-scaled production of such heterocyclic monomer and prepolymer systems. Herein, the continuous high shear reactor that is utilized has the ability to feed reactants independently, for staged reaction cascade, or for a preblended batch approach. Moreover, the novel methods provide the ability to control the temperature, time, and shear in the processing section. The control and feed system features of the invention enable the ability to produce high volumes of heterocyclic monomer alloys and prepolymer alloys with predictable prepolymer conversion and reduced isomer content and to eliminate the need for post-processing purification via a cost-effective and environmentally-favorable one-step method.
Heterocyclic chemistries such as benzoxazines have previously been synthesized in solvent-free and single-screw reactors. However, a single-step, solvent-free synthesis methodology of heterocyclic monomer (monofunctional and/or multifunctional) and prepolymer alloy production with increased reaction efficiency and elimination of post-processing purification is unreported in the current scientific and patent literature. The present invention provides such novel methodologies whereby a continuous, high shear reactor is comprised of at least one co-rotating twin-screw extruder, which is highly modular with respect to structural design, feed delivery systems, and experimental parameters, for example, but not limited to processing temperature, residence time, screw speed, and/or screw design.
The solvent-free, continuous high shear reactor methods and system of the present invention provide a cost-effective, environmentally-favorable, and scaleable method to synthesize heterocyclic monomer and prepolymer alloys. The invention alternatively can be utilized in-solvent.